The long-term goals of this project are to understand the mechanical basis for activation of stretch-sensitive mechanoreceptor neurons (Ruffini afferents) that are located in skin and joint capsules. Understanding the basis for the activation of these afferents will allow us to use the neurons as a probe to make measurements of local biomechanical states in both skin and joint capsule. One goal is to determine whether stretch sensors in the joint capsule respond in relation to compression stresses and strains. We will test an hypothesis that sensitivity to axial stress is mediated through the transverse (Poisson) compression that results from axial deformations. A second goal is to determine the states of biaxial stress and strain that are related to afferent discharge, using biaxially loaded sheets of tissue. Two different preparations will be used in these studies: a. In a preparation of isolated rat skin, we will study the properties of cutaneous SAII afferents. Because this tissue is a uniform sheet, there is great flexibility in creating known states of stress and strain. b. In a preparation of isolated joint capsule from the cat knee. The specific goal is to understand what mechanical states are encoded by the neurons, and to use the neurons to determine the local states that are present in various types of joint loadings. A third goal is to develop micromechanical models of the neuron/tissue interaction that are consistent with the observed response to macroscopic stimuli.